Full Idea
The symbols for classes are mere conveniences, not representing objects called 'classes'. Classes are in fact logical fictions; they cannot be regarded as part of the ultimate furniture of the world.
Gist of Idea
Classes are logical fictions, and are not part of the ultimate furniture of the world
Source
Bertrand Russell (Introduction to Mathematical Philosophy [1919], Ch.18), quoted by Stewart Shapiro - Thinking About Mathematics 5.2
Book Reference
Shapiro,Stewart: 'Thinking About Mathematics' [OUP 2000], p.123
A Reaction
I agree. For 'logical fictions' read 'abstractions'. To equate abstractions with fictions is to underline the fact that they are a human creation. They are either that or platonic objects - there is no middle way.